This application claims the priority of German application 196 51 625.0 filed in Germany on Dec. 12, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a heat transfer device, particularly a charge air cooler in a stack construction, having a finned-tube block which is constructed of several layers of ducts for the coolant flowing through, which extend in parallel to one another, and of lamella-type corrugated fins which are in each case inserted between these layers and which, in the area of the ends of the ducts leading into the coolant tanks, each rest against supporting fins of end strips which are inserted between adjacent layers of ducts for forming the tube bottom.
Heat transfer devices of this type and their finned-tube blocks are subjected to very high change-of-temperature stress. It is known that, in the case of charge air coolers, as used, for example, for large 2,000 kW engines or for high-power engines for utility vehicles, charge air temperature of a magnitude of 235.degree. C. or more occur on the inlet side during the full-load operation. In the case of known heat transfer devices of this type (German Patent Document DE-OS 23 42 787), it cannot be prevented that the ducts expand relatively fast on the air inlet side. The thermal expansion has the result that local tension peaks occur at the soldered joints between the end strips and the ducts, which tension peaks may result in damage during frequent load changes and thus in a shorter useful life of the finned-tube blocks.
It is an object of the present invention to develop a heat transfer device of the initially mentioned type such that the mentioned local tension peaks can be avoided.
For achieving this object, it is provided according to the invention that, in the case of a heat transfer device of the initially mentioned type, the lateral surfaces of the end strips resting against the ducts form the exterior surfaces of lips projecting in the direction of the corrugated fins, the points of these lips not contacting the corrugated fins and their cross-section increasing uniformly toward the side facing away from the corrugated fins.
Because of the absence of an abrupt jump of the cross-section at the transition between the supporting fins and the ducts, this further development achieves a clear reduction of the local tension peaks and thus also a reduction of the component load in the tube bottom area. As a result, the useful life of heat transfer devices of the initially mentioned type can be extended.
As a further development of the invention, one groove respectively may be formed between the lip and the supporting fin, in which case the wall of the groove pointing to the lip may form a parabolically curved surface. It was found that by means of such a further development the desired uniform increase of the cross-section of the exterior lip is achieved and, as a result, tension concentrations and undesired tension peaks are avoided.
As a further development of the invention, each end strip may have a supporting fin which is arranged in the center and whose width amounts to approximately one third of the width of the end strip. In a simple manner, the supporting fin may have a rectangular cross-section. End strips of the type used for the invention can easily be made, for example, of aluminum by means of extruding. It was found to be particularly advantageous for these end strips to consist of an aluminum magnesium alloy.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.